Biochemical and spectroscopic analysis of the effect of UV on the pigmentation of the red algae Gracilaria dentata, Hypnea musciformis and Centroceras clavulatum

Red algae are multicellular organisms that belong to the family Rhodophyceae. Majority of them are found at a depth of 40 m, where only short-wavelength visible light penetrates in any significant intensity and can be absorbed by red algae. The objective of this study was to determine the sensitivity of Gracilaria dentata, Hypnea musciformis and Centroceras clavulatum to components of solar spectrum and their survival. Specifically, effects of UV-A, UV-B and PAR on pigmentations of Gracilaria dentata, Hypnea musciformis and Centroceras clavulatum were investigated under laboratory conditions. Thalli of the algae were exposed either to unfiltered solar radiation or solar radiation filtered through WG 295, WG 320, and GG 400 cut-off filters. Sucrose gradient ultracentrifugation revealed that all the organisms had allophycocyanin as accessory pigment in addition to phycoerythrin and phycocyanin. The phycoerythrin occurred in monomers, trimers, and hexamers. Results from SDS-PAGE analyses of the protein profile of the organisms revealed a loss of high molecular weight proteins and that of low molecular weight proteins (a and b monomers), indicating a breakdown of the phycobilisomal complex and impaired energy transfer from accessory pigments to the reaction centres of photosystems. Although the photosynthetic pigments of the organisms were drastically degraded, Hypnea musciformis appeared to be more resistant compared to Gracilaria dentata and Centroceras clavulatum. The SDS-PAGE analyses clearly indicated that organisms exposed to unfiltered solar radiation and PAR+UV-A+UV-B were destroyed as shown by the polypeptide bands intensities. Hypnea musciformis, the least bleached, could be used as a reference resistant organism for future studies. The adverse effects of the various components of UV radiation on photosynthetic pigmentation and composition of phycobiliproteins of the red algae indicate the potential deleterious effects of UV-radiation on marine organisms.